Search for and characterization of temperature-sensitive Chinese hamster cells a) one report has been published: Scheffler, I.E. and G. Buttin (1973) J. Cell. Physiol. 81,199-216. b) Some further investigation of the mutant described above is planned, particularly involving cellular hybridizations. c) The search for more such mutants of interest for the study of the cell cycle, DNA synthesis, and cell division is under way and to be pushed, manpower permitting. A paper describing a mutant defective in pyruvate metabolism has been submitted to J. Cell. Physiol. The mutation is conditionally lethal, the cells being able to grow in the presence of bicarbonate and CO2. Studies are in progress to pinpoint the defect in one of the enzymes responsible for the entry of pyruvate into the tricarboxylic acid cycle.